desktop-shell: background should be opaque
desktop-shell: background should be opaque

Toytoolkit does not support setting opaqueness for anything else than
the immediate child widget of the frame widget. Backgrounds do not have
frames, so we need to poke it in manually.

This should allow Weston to paint the background without blending.

Signed-off-by: Pekka Paalanen <6c0263d81461c956d504307112a4ce25eaacc3d1@gmail.com>

Fantu/compositor-spice,giucam/weston,Fantu/compositor-spice,krezovic/weston,sir-murray/weston,kwm81/weston,udoprog/weston,Tarnyko/weston-xdg_surface_present,xorgy/weston,mchalupa/weston,mchalupa/weston,Tarnyko/weston-xdg_surface_present,eyolfson/weston,sir-murray/weston,xorgy/weston,udoprog/weston,jonnylamb/weston,Gnurou/weston,giucam/weston,Fantu/compositor-spice,krezovic/weston,Gnurou/weston,eyolfson/weston,kwm81/weston,jonnylamb/weston